Question

How to solve y-x=0 and 7x-9y=8 by substitution

Answer 1

With y-x=0, add x to both sides to get y=x.

Now you can substitute either x or y

7x-9x=8 or 7y-9y=8 which is the same thing

-2x=8 or -2y=8

x=-4 or y=-4

Hope this helped!